Discovery’s Manhunt: Unabomber is halfway through its season, and in tonight’s fifth hour, FBI profiler Jim “Fitz” Fitzgerald (Sam Worthington) finally learns the name of the man he’s been looking for: Ted Kaczynski (Paul Bettany). As you see in the sneak peek above, Ted’s brother, David (Mark Duplass), doesn’t want to speak with Fitz because he and his wife, who were afraid they recognized Ted’s voice in the 35,000-word manifesto printed in the Washington Post, flagged Ted for the FBI and were told it wasn’t him. But that’s because the bureau still doesn’t believe in Fitz’s fledgling field of forensic linguistics.

Needing to cast someone who could interpret the layers of David’s struggle, producers found Duplass, who was in the midst of penning the upcoming memoir Like Brotherswith his sibling, Jay, his co-creator on the new HBO anthology series Room 104, and could connect with the idea of having a complex relationship. “My brother and I have been best friends and soulmates and business partners on and off for 40 years. And when I imagine the sort of guilt and complex emotions that David would have about essentially being the one who turned Ted in, that felt like one of the things that I could plop myself into fairly easily,” Duplass says. “In some ways, you’d think that you need tons and tons of time to ‘prepare’ to play a real-life person; this was one of the easiest roles to prepare for from an emotional standpoint, because I have all of that stuff with my brother to draw upon.”

What was challenging — as it is for any series exploring the making of a domestic terrorist — was striking the right tone. It’s a fine line to walk, for instance, with both David and Fitz admitting they admire that Ted had enough conviction in his antitechnology ideals to move out to his Montana cabin, while of course emphatically abhorring the actions he took to force others to hear them.

Duplass and director-showrunner Greg Yaitanes tried to focus on the fact that David very easily could have ended up becoming Ted, and Ted very easily could have ended up becoming David. “They were following a very similar path of highly intelligent, socially awkward, quirky individuals, who had high, high ideals, and at a certain point, Ted could not compromise those things and went all the way. And at a certain point, David learned how to compromise those things and have a normal life,” Duplass says. “But David feels very guilty about that for a number of reasons. And that was sort of the touchstone for me — there’s a little bit of a sliding doors element with David and Ted. At least the way I approached it, David is like, ‘I could have ended up being that, and maybe I should have done more to stop my brother from being that.’ And that’s a tough way to feel.”

Worthington suspects it was also challenging working with him in those scenes, when Fitz could feel he was so close to getting something that he could use to tie Ted to the manifesto (letters Ted had written David over the years). “Every take I was just on him and on him and on him and on him, as if it was Gollum going for the ring, going for his Precious. It’s really annoying when I go for someone. I don’t stop,” Worthington says. “They’re even going ‘Cut!’ and I keep going and going and going. Mark must be thinking, ‘This guy’s insane.’ He must have thought I was just a really annoying actor who wouldn’t stop and wouldn’t take no for an answer, and Greg was great — he let us have the freedom to improvise and the freedom for me just to push. He never got in the way. He just said, ‘Sam’s going to come at you. You got to deal with him.'”

“He’s a full-on maniac,” Duplass says in response. “No, I mean, I’m used to that. I come from an improvised background on the show called The League where we literally just improvised the entire show off an outline. So that’s fun to me. But Sam’s a real process-oriented guy, and you could tell it was always an internal fight with him to try to find the right moments. And that was part of my job on this set; when you are not the lead character in a show, you have to do what you need to do to support those leading characters. David’s story is fascinating, but this, in a lot of ways, is really the story of Fitz. So I’m more than happy to lay the ball up so that Sam can take it and dunk it. That’s what you do there.”

Switching gears for Room 104, Mark and Jay are the leading creative forces behind that show, which each week tells a different story, in a different genre, in the same hotel room. Mark wrote this Friday’s episode, “The Internet,” which for the first time takes the series back in time.

“It is heavily based on a true experience I had with my own mother, which started out as a very funny conversation trying to teach her how to do email over the phone and ended up with the two of us almost killing each other and never speaking to each other again,” he says. “I felt like it was time to bring it to light. It stars one of my close friends, Karan Soni, who you’ll recognize as sort of this really funny character actor. He’s in Deadpool. He’s in Ghostbusters. He’s always that quirky Indian or Pakistani guy who kills for 10 minutes as a side character, and I really wanted to give him his first leading role because he’s very funny but he’s also incredibly soulful and beautiful. And so almost the entire episode is just him in this room.”

It’s the fifth installment of the anthology series, which will finish its 12-episode season in October with another half-hour penned by Mark, “My Love.” It’s about an elderly couple who revisit the room where they spent their first night together 56 years ago.

“It’s very quiet and it’s very simple,” he says. “Every time you think you know what the show is, you get surprised by something. And so those of you who are like, ‘Yes! This is a f***ed up late night show,’ it is. But it’s other things, too. And ‘My Love’ is certainly an example of something that you might not expect after you’ve watched an episode like ‘Ralphie’ [the bloody series premiere], for instance.”

What has he learned working in all these different genres that the Duplass brothers (Togetherness) may not be known for? “The takeaway so far is it’s really, really fun to play in them, and as long as we hire directors who know what they’re doing, I don’t get afraid,” Mark says.

And, in light of The X-Files recently making headlines for having just two of its next 10 episodes slated to be directed by women, it’s worth noting that eight episodes of Room 104′s season have female directors.

“We don’t want to pat ourselves on the back and be like, ‘Look at us! Look how inclusive we are!’ Truth is, these are incredibly talented directors, and I’m lucky to have them,” Mark says. “I do think it’s important now to consider representation, both in front of and behind the camera, and we did consider that. But we never ever said, ‘Oh gosh, we should hire some more women, so let’s just hire this person.’ It was always, ‘Let’s hire some really, really talented people, and wouldn’t it be nice if we could have more female directors because that’s not happening enough.’ It was a pretty organic and easy decision.”